combine.c (nonzero_bits): Allow single-ly set registers to be anywere in the function...

	* combine.c (nonzero_bits) : Allow single-ly set registers to be
	anywere in the function only if they are pseudos and set before
	being used (not live at the start of the function).
	(num_sign_bit_copies) : Same.
	(get_last_value_validate) : Same.
	(get_last_value) : Same.

From-SVN: r28871

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 30a31f2..a5ea729 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,12 @@
+Wed Aug 25 15:27:22 1999  Gavin Romig-Koch  <gavin@cygnus.com>
+
+       * combine.c (nonzero_bits) : Allow single-ly set registers to be
+       anywere in the function only if they are pseudos and set before
+       being used (not live at the start of the function).
+       (num_sign_bit_copies) : Same.
+       (get_last_value_validate) : Same.
+       (get_last_value) : Same.
+
 Wed Aug 25 11:13:29 1999  Richard Henderson  <rth@cygnus.com>
 
        * loop.c (express_from): Try harder to unify (* c N) and (* c M)

diff --git a/gcc/combine.c b/gcc/combine.c
index b2c3f50..dcd60c2 100644 (file)
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -7521,8 +7521,11 @@ nonzero_bits (x, mode)
 
       if (reg_last_set_value[REGNO (x)] != 0
          && reg_last_set_mode[REGNO (x)] == mode
-         && (REG_N_SETS (REGNO (x)) == 1
-             || reg_last_set_label[REGNO (x)] == label_tick)
+         && (reg_last_set_label[REGNO (x)] == label_tick
+             || (REGNO (x) >= FIRST_PSEUDO_REGISTER
+                 && REG_N_SETS (REGNO (x)) == 1
+                 && ! REGNO_REG_SET_P (BASIC_BLOCK (0)->global_live_at_start, 
+                                       REGNO (x))))
          && INSN_CUID (reg_last_set[REGNO (x)]) < subst_low_cuid)
        return reg_last_set_nonzero_bits[REGNO (x)];
 
@@ -7911,8 +7914,11 @@ num_sign_bit_copies (x, mode)
 
       if (reg_last_set_value[REGNO (x)] != 0
          && reg_last_set_mode[REGNO (x)] == mode
-         && (REG_N_SETS (REGNO (x)) == 1
-             || reg_last_set_label[REGNO (x)] == label_tick)
+         && (reg_last_set_label[REGNO (x)] == label_tick
+             || (REGNO (x) >= FIRST_PSEUDO_REGISTER
+                 && REG_N_SETS (REGNO (x)) == 1
+                 && ! REGNO_REG_SET_P (BASIC_BLOCK (0)->global_live_at_start,
+                                       REGNO (x))))
          && INSN_CUID (reg_last_set[REGNO (x)]) < subst_low_cuid)
        return reg_last_set_sign_bit_copies[REGNO (x)];
 
@@ -10734,9 +10740,11 @@ get_last_value_validate (loc, insn, tick, replace)
 
       for (j = regno; j < endregno; j++)
        if (reg_last_set_invalid[j]
-           /* If this is a pseudo-register that was only set once, it is
-              always valid.  */
-           || (! (regno >= FIRST_PSEUDO_REGISTER && REG_N_SETS (regno) == 1)
+           /* If this is a pseudo-register that was only set once and not
+              live at the beginning of the function, it is always valid.  */
+           || (! (regno >= FIRST_PSEUDO_REGISTER 
+                  && REG_N_SETS (regno) == 1
+                  && ! REGNO_REG_SET_P (BASIC_BLOCK (0)->global_live_at_start, regno))
                && reg_last_set_label[j] > tick))
          {
            if (replace)
@@ -10795,12 +10803,21 @@ get_last_value (x)
   regno = REGNO (x);
   value = reg_last_set_value[regno];
 
-  /* If we don't have a value or if it isn't for this basic block,
-     return 0.  */
+  /* If we don't have a value, or if it isn't for this basic block and
+     it's either a hard register, set more than once, or it's a live
+     at the beginning of the function, return 0.  
+
+     Because if it's not live at the beginnning of the function then the reg 
+     is always set before being used (is never used without being set).
+     And, if it's set only once, and it's always set before use, then all
+     uses must have the same last value, even if it's not from this basic
+     block.  */
 
   if (value == 0
-      || (REG_N_SETS (regno) != 1
-         && reg_last_set_label[regno] != label_tick))
+      || (reg_last_set_label[regno] != label_tick
+         && (regno < FIRST_PSEUDO_REGISTER
+             || REG_N_SETS (regno) != 1
+             || REGNO_REG_SET_P (BASIC_BLOCK (0)->global_live_at_start, regno))))
     return 0;
 
   /* If the value was set in a later insn than the ones we are processing,